There is a critical need to identify risk factors associated with increased suicidality in Veterans. Nonsuicidal self-injury (NSSI) refers to the deliberate destruction of body tissue without conscious intent to die. Among civilians, recent evidence suggests that NSSI is a robust predictor of suicide attempts, outperforming a number of well-established risk factors in prediction models. Patients with NSSI Disorder also report great functional impairment and higher levels of treatment utilization than psychiatric patients without NSSI Disorder. However, to date, this important clinical issue has been largely overlooked among Veterans. We recently documented alarming lifetime rates of NSSI among help-seeking Veterans. Specifically, we found that 57-66% of male Veterans seeking treatment for PTSD endorsed lifetime NSSI, and 45-55% reported engaging in NSSI during the previous two weeks. We have also shown that NSSI is uniquely associated with suicidal ideation in Veterans, even after accounting for PTSD and depression. More work is needed to: (1) Define the long-term functional outcomes associated with NSSI and NSSI Disorder in Veterans, and (2) Identify modifiable treatment-relevant mechanisms that maintain NSSI in Veterans. This knowledge will be a critical first step toward our long-term goal, which is to develop effective screening and intervention strategies that will reduce NSSI and other forms of self-injurious behavior (i.e., suicidal behavior) among Veterans. The overall objective of this application is to identify the long-term effects of NSSI on Veterans? functioning as well as the specific antecedents and consequences that maintain this destructive behavior. Consistent with our conceptual model, our central hypothesis is that NSSI is preceded by exacerbations in psychiatric distress and maintained through both intrapersonal (e.g., temporary reductions in psychiatric symptoms) and interpersonal reinforcement (e.g., increased attention from others). The rationale for the proposed research is that the identification of factors that underlie and maintain NSSI in Veterans will facilitate the development of treatment approaches that are specific to the needs of these Veterans. In Aim 1, we will conduct a 1-year longitudinal study of Veterans with a history of recent NSSI (N = 120) to evaluate the long-term functional outcomes associated with this destructive behavior. We hypothesize that baseline NSSI frequency and baseline NSSI Disorder status will prospectively predict increased functional disability, greater treatment utilization, increased suicidal behavior, and increased NSSI frequency at 1-year follow-up after accounting for psychiatric comorbidity and known risk factors. In Aim 2, we will use ecological momentary assessment (EMA) to identify antecedents that predict the occurrence of NSSI as well as the consequences that serve to maintain this behavior in a subset of Veterans from Aim 1 who meet criteria for NSSI Disorder (N = 40). We hypothesize that increases in psychiatric distress and NSSI-related motives will be significant antecedents of NSSI episodes. We further hypothesize that NSSI episodes will be associated with temporary reductions in psychiatric distress and temporary increases in positive affect and social support. Together, these studies will provide critical data on key factors that contribute to the initiation and maintenance of NSSI and will guide future treatment development efforts aimed at reducing the occurrence of NSSI and other forms of self-injury (i.e., suicidal behavior) among Veterans.